In the construction of current limiting fuses for application outdoors, it is desirable to have a design which is impervious to the entrance of moisture. Moisture inside of a fuse could cause a malfunction when called upon to clear a fault occurring on the electrical system. Malfunction of the fuse could be caused by the heat of the arc in the fuse turning the moisture therein to steam with sufficient internal pressure to rupture the fuse housing. Moisture can also cause the dielectric strength of the internal parts of the fuse to degrade to a level which would allow tracking and flashover to occur during high voltage withstand following fuse interruption of a fault current.
Current limiting fuses presently available generally require an electric current interchange between the fuse assembly and the end caps of the fuse. This interchange is generally provided by tabs on the winding assembly protruding through openings in the end caps and being soldered to the end caps or alternately having one of the fuse elements of the winding assembly protruding through an opening in the cap and being soldered to the end cap. In both of these examples, the end cap integrity against ingress of moisture has been violated by the openings provided in the end cap. The openings may be sealed during production by soldering but over a period of years, leaks may occur due to physical deterioration of the solder in the opening. When the soldering is done after the fuse has been assembled, the heat used during soldering can expand the end cap at a faster rate than the nonmetallic fuse tube stressing the epoxy joints and producing leakage.
Flexible conducting metal tabs attached to the end plates have been used to provide electrical connections to the end caps. The tabs are bent to engage the end caps which produces a compression fit. This produces a compression connection which is hard to control due to production tolerances of the parts. Where the flexible conducting metal tabs have been used to provide electrical connection to the end caps, failures have also occurred due to the relaxing or cold flow of the compression joints over a period of years.